The present invention relates to the separation of actinides, including for example americium, from radioactive waste solutions.
A number of nuclear processes generate spent nuclear fuel with high levels of radioactive decay. At present, spent nuclear fuel is stored among reactor sites in approximately 39 different states across the U.S., and largely without recycling or reprocessing. For example, as much as 59,000 tons of spent nuclear fuel are in temporary storage, growing at a rate of 2,300 tons per year. Over the past several decades, however, efforts have been underway to centralize the disposal of current and future spent nuclear fuel into a single repository. To maximize the capacity of a single repository, methods have been proposed to recycle portions of spent nuclear fuel, thereby minimizing the quantity of spent nuclear fuel intended for long term storage.
For example, processes such as Uranium Extraction (UREX) and Plutonium Uranium Recovery by Extraction (PUREX) have been developed to extract uranium and/or plutonium from spent nuclear fuel for use in commercial reactors using liquid-liquid reprocessing techniques. After these extraction processes, however, a number of highly radioactive constituents remain. After UREX reprocessing, for example, the remaining constituents include plutonium (Pu) and several minor actinides, including americium (Am), neptunium (Np) and curium (Cm). Am constitutes approximately 73% of all the minor actinides present after fifty years of storage. In addition, Am-241 generates approximately 75% of the emitted heat after 250 years of storage, while its decay daughter, Np-237, is the principal source of radiotoxicity among the remaining minor actinides.
The amount of spent nuclear fuel that can be stored in any single repository is generally constrained by the amount of decay heat and radiotoxicity generated by the constituent actinides. As the decay heat and radiotoxicity of constituent actinides increase, the spacing between storage units within the repository must also increase. Thus, it is generally desirable to eliminate or severely reduce the presence of actinides, and most significantly Am, from spent nuclear fuel.
Accordingly, there remains a need for an improved system and method for the separation of actinides from spent nuclear fuel. In particular, there remains a need for an improved system and method for the separation of americium from an aqueous waste solution to minimize the heat decay and radiotoxicity of spent nuclear fuel for long term storage solutions.